Apparatus for the production of aqueous dispersions of solids insoluble in water



Nov. 14,1967 H, H, MQLLS ET AL 3,352,500

APPARATUS FOR THE PRODUCTION OF AQUEOUS DlSPERSIONS OF SOLIDS INSOLUBLEIN WATER Filed Oct. 7, 1964 2 Sheets-Sheet 1 [-76.7 FIG.)

77 "1/3 i 1 I 6 7 I i H 6:( 4a

INVENTORS.

ERICH MULLER.

A TTORNEY Nov. 14,1967 H. H. MOLLS ETAL 3,352,500

APPARATUS FOR THE PRODUCTION OF AQUEOUS D ISPERS IONS OF SOLIDSINSOLUBLE IN WATER Filed om. 7, 1964 2 Shets-Sheet 2 INVENTORS: H, HEINZMOTLLS, RE/NHOLD HURNLE, HANS RAAB, ER/CH MULLER.

ATTORNEY United States Patent APPARATUS FOR THE PRODUCTION OF AQUE- OUSDISPERSIONS 0F SOLIDS INSOLUBLE IN WATER Hans Heinz Miills and ReinholdHiimle, Cologne-Flittard, Hans Raab, Cologne-Stammheim, and ErichMiiller, Bergisch-Neukirchen, Germany, assignors to Farbeni'abrikenBayer Aktieugesellschaft, Leverkusen, Germany, a German corporationFiled Oct. 7, 1964, Ser. No. 402,213 1 Claim. (Cl. 241-74) It is knownthat solids, for instance dyestuffs, can be finely subdivided in anaqueous or organic medium by means of agitated rounded grinding elementsof quartz, glass, ceramics, metals or plastics, optionally in thepresence of dispersing agents (cf. for instance Swiss patentspecification No. 132,086; German patent specifications Nos. 619,662 and915,408 and German published specification No. 1,109,988; Belgian patentspecification No. 588,161, British patent specification No. 909,609 andUS. patent specifications Nos. 2,212,641, 2,361,059 and 2,581,414). Theefiiciency of a process of this type depends on the kind and intensityof the agitation imparted to the grinding elements, on the relationbetween the volume of the grinding elements and that of the suspension,on the concentration of the solid in the suspension and on the type andamount of the added tensides (surface active agents). The selection of asuitable dimension for the grinding elements largely depends on theinitial particle size of the grinding stock.

Solids, for instance dyestufis, have already been finely subdividedaccording to the process of US. patent specification No. 1,837,772 bystirring the solids in an aqueous or non-aqueous medium, in the presenceof a dispersing agent, with solid grinding elements in an open vessel.Anion active dispersing agents such as the sodium salt ofdinaphthylmethane-2,2-disulphonic acid, the sodium salt of sulphitecellulose and its oxidation product, as well as amidated sulphitecellulose and sodium benzylsulphonate have already been employed as thedispersing agents. Compact insoluble powders which are harder than thematerial to be finely subdivided or dispersed are recommended as thegrinding elements, for instance iron powder, zinc powder, copper powderor sand with a maximum particle size of 0.125 mm.

The last mentioned process has not been adopted in practice, and neitherhave the previously cited processes except that of U.S. patentspecification No. 2,581,414, because no appreciable advantages inrespect of the fine subdivision of the grinding stocks were evident incomparison with the customary methods of subdivision -(for instancewithout solid insoluble auxiliary grinding elements) in the usual ballmills with grinding elements of a comparable size. The above mentionedprocesses also do not offer any improvement in respect of a saving ineffort (time requirement). The application of the only process adoptedin practice (US. patent specification No. 2,581,- 414) is limited to thepreparation of dispersed pigments in non-aqueous film forming media.Aqueous pigment pastes, such as are for instance obtained during themanufacture of pigment dyestuffs, cannot be processed according to theprocess of this patent in order to form finely dispersed dyestuffs.

In all known grinding devices with small grinding elements, theagitation of the grinding mixture leads to the formation of turbulentcurrents at the interface between the air (or gas) and the dispersion ofthe grinding stock or the grinding mixture, so that air (or gas) isaspired into the grinding mixture. This circumstance exerts aparticularly unfavourable effect on the grinding action or on thedispersion of solids insoluble in water when use is made of thosedispersing agents which exhibit a stronger 3 ,352,500 Patented Nov. 14,1967 ice tendency towards the formation of foam. Strong formation offoam takes place in particular during grinding with small grindingelements under these conditions, and owing to the resultant air cushioneffect the mobility of these small grinding elements is impeded, so asto cause a decrease of the grinding action down to a technically uselessvalue and frequently so as to cause difficulties during the separationof the grinding stock from the grinding elements; flotation of thegrinding elements is also often experienced during this operation.

A large number of dispersing agents which exhibit a particularly gooddispersing action unfortunately have a tendency to form the kind of foamdescribed above. Such dispersing agents may already have originated fromthe process for the production of the solids or their presence may alsobe generally desirable in order to achieve a fine dispersing action bymeans of suitable devices. Therefore, technologists do not in practicelike to dispense with the application of such agents, and as aconsequence a large number of devices for the fine subdivision ofpigments have not been successfully adopted for this reason alone.

The dispersing devices of US. patent specification No. 2,5 81,414 and ofGerman published specification No. 1,109,988 intended for non-aqueousdispersion are also unsuitable for processing dispersions containingsubstances which promote strong foaming; they aspire air on the top sideof the uppermost disc or of the uppermost ring as well as on thevertical sieve, and this air passes through the whole grinding systemwithin a short time so as to cause appreciable foaming. The reducedseparation at the sieve basket and the flotation of the grindingelements causes the foam-charged grinding mixture to spill over theupper edge of the sieve.

Processes and devices for the dispersion in an aqueous medium of organicand inorganic solids insoluble in Water have now been found which do notexhibit the disadvantages known to occur during processing in an aqueousmedium by means of the devices known as sand mills and comparableappliances, and these permit the attainment of optimum results even whenstrongly foam-forming dispersing agents are applied. The novel processutilises a number of known factors, by agitating an organic or inorganicsolid insoluble in water in an aqueous medium with a dispersing agentand a material containing silicon dioxide groups whose specific gravityis greater than 1.5 and which is harder than the product to bedispersed; it is characterised in particular in that rounded elementswhose radii do not differ by more than i40% from the mean radius, whichhave a smooth surface, whose diameters are from 0.3 to 1.5 mm. and wherethe particle diameter does not differ by more than 0.5 mm. from the meanvalue are employed as the material containing silicon dioxide groups, ina proportion of 10 to 300% of the solid volume, referred to the volumeof the dispersion of the grinding stock; in that non-ionic, anionic,cationic or betaine-type dispersing agents are employed in a proportionof 0.1 to 200% by weight, referred to the weight of the solid to bedispersed, optionally in conjunction with defoaming agents; and in thatthe agitation of the grinding mixture is continued until the particlesize of the grinding stock is 6,u or preferably less; in the case Whereuse is made of those dispersing agents which increase the volume of thegrinding stock during the grinding operation by more than 20%, and inparticular by more than 50%, as a. consequence of their capacity for theformation of foam, the grinding operation is carried out in anarrangement of apparatus such that no appreciable air (or gas) aspiringcurrents can possibly be formed at the interface between the air (orgas) and the dispersion of the grinding stock or the grinding mixture.

The terms grinding stock, dispersion of the grinding stock, grindingelements and grinding mixture are here employed in accordance with thefollowing definition's: the grinding stock is the solid to be dispersed;the dispersion of the grinding stock is the aqueous dispersion of thegrinding stock which may optionally contain dispersing agents; thegrinding elements are the rounded elements containing silicon dioxidegroups; and the grinding mixture is the mixture of the dispersion of thegrinding stock with the grinding elements.

The agitation of the grinding mixture during the proc ess according tothe invention is effected so that the highest possible velocity gradientexists between the grinding elements without causing the grindingelements to become squashed at any point in the grinding mixture. Itshould not be possible for the grinding stock to escape from the actionof the grinding elements within the grinding device.

By Way of grinding appliances which cause an air aspiring turbulence atthe surface of the grinding stock or grinding mixture, falling, tumblingand turbine mixers may be employed, such as have for instance beenlisted in Ullmann: Encyclop'zidie der technischen Chemie (Urban undSchwarzenberg Verlag, Munich-Berlin), 3rd edition, volume I (to bereferred to as Ullmann I hereafter) on pages 714-715. In addition,stirrer mixers have been employed, where suitable mixing elements at alow number of revolutions (at circumferential speeds of 1-4 m./ sec.)are for instance those specified in Ullmann I on page 707. Owing to therisk of abrasion and the possibility that the grinding elements may bedestroyed, only stirrers with plane crossed blades, stirrers with astreamline cross section, stirrer screws and also stirrers with one orseveral flat or conical compact or perforated circular discs or ringsconnected to the shaft by spokes are suitable at circumferential speedsgreater than 4 m./sec.; the circular discs or rings should be attachedvertically to the stirrer shaft and the shaft should pass through theircentre. In the case where several mixing elements are employed, theyshould be spaced at a distance of roughly between their half and theirfull radii in their attachment to the stirrer shaft. The circumferentialspeeds should be between 4 and 20 m./sec., preferably between 7 and 13m./sec. In addition, oscillatory mixers operating at moderatefrequencies (Ullmann I, p. 722) and vibrating mills operating at highfrequencies such as have for instance been specified in Ullmann I onpage 725 are also suitable.

Moreover, the agitation of the grinding mixture can be effected by meansof a vibro mixer with the use of one stirrer plate or of several stirrerplates arranged on top of each other as the mixing elements (Ullmann I,p. 702) at frequencies of 50-100 cycles/ sec. and an amplitude ofpreferably 23 mm. The diameter of the conical apertures at the narrowestpoint in the stirrer plates should amount to between 4 and 16 times themean diameter of the grinding elements. In the case where severalstirrer plates are employed, these should be spaced at a distance ofroughly between their quarter and their full radii in their attachmentto the shaft.

When grinding devices of this type are operated discontinuously, theaspiration of gas or air at the interface between the grinding mixtureor grinding stock and thegas or air can sometimes be prevented bycarrying out the grinding operation at a reduced pressure of preferablyless than 200 mm. Hg.

The formation of foam may also be eliminated during a discontinuousoperation by carrying out the process in sealed vessels which arecompletely filled with the grinding mixture, although this form ofexecution can only be applied when there is no appreciable resultantdeterioration of the grinding action.

The arrangement of apparatus in machines with a continuous operation issuch thatno appreciable turbulent current of air (or gas) aspiration canoccur at the interface between the air (or gas) and the dispersion ofthe grinding stock or the grinding mixture.

The machines with a continuous operation do not differ from theappliances with a discontinuous operation which have already beenmentioned abo e. i respect Of the elements has to be fitted in front ofthe discharge outlet in order to retain the grinding elements. Theprevention of a turbulent current of aspired air or gas can be effectedin front of or beyond the sieve, when the constructions representeddiagrammatically in FIGURES 1-5 are preferably employed.

In FIGURES 1-5, 1 represents a cylindrical grinding vessel surrounded bya cooling or heating jacket 2; a shaft 3 carrying the mixing elements 4,which have in the given case been drawn in the form of discs, extendsconcentrically into the grinding vessel. The grinding vessel is providedwith an inlet 5 for the coarse dispersion which has to be ground, thisbeing connected to'a liquid pump and optionally provided with a devicefor preventing the backfiow of the grinding mixture. The dischargeoutlet 6, which is an overflow in the case of FIG. 1 and FIG. 2, isprovided beyond a sieve 7, in relation to the position of the grindingmixture, and this is preferably adjoining the free side of the grindingvessel. The design of the sieve 7 in FIGURES 2-5 may also be modified inthat the part of the sieve which is either perpendicular 7a to the shaft3 or parallel 7b with it is replaced by a compact surface when in thesecond case the cooling jacket 2 is raised up to the level of the sieve7a. The mesh width of the sieve has to be selected so that the smallestemployed grinding elements are just prevented from passing through it. p

The inner surfaces of the grinding vessel 1 and of the sieve 7 enclosethe grinding space 8, although the corn str-uction according to FIG. 1constitutes an exception in that the horizontal plane extending from theupper edge of the overflow represents the upper limit of the grindingspace in this non-enclosed system. The grinding space is completelyfilled with the grinding mixture when the dis- 7 V persion of the solidwhich has to be ground is pumped through it. The grinding space andwhere required the external surfaces are sealed by means of seals 10 atthe locations where the shaft 3 penetrates through them, and these mayalso act as bearings. The seal 10 may for instance be of rubber, metal,graphite, plastics or sealing liquid, and in the last case thedispersion of the grinding stock rising above the upper surface of thesieve 7a may also act as the seal, as may the grinding mixture itself ina suitable construction, for instance if a sieve or pipe is passed roundthe shaft.

The grinding mixture is agitated by stirring (rotation) or by vibration.When the agitation is effected by stirring, the grinding space contains30 to 70, and preferably 40 to 60, percent of the solid volume of thegrinding elements in relation to the free volume; in that case, thestirrer mixers mentioned in column 3 are employed as the mixingelements, when the distance between the mixing element and the grindingvessel in each case depends on the diameter of the grinding elements andshould amount to between 3 and 30 times the diameter of the grindingelements.

The aspiration of air or gas into the grinding mixture at the interfacebetween the grinding mixture or the dispersion of the grinding stock andthe air or gas 9 which occurs to an extremely marked extent in thenormal constructions of high speed stirred ball mills With circulardiscs or rings on spokes is prevented in the case of the form ofexecution according to FIG. 1 by replacing the uppermost stirrer element4a by a compact cylinder 11 whose radius is of about the same magnitudeand by placing the overflow 6 for the dispersion of the grinding stockat an appreciably higher level than the lower side of the sieve 7. Thelower surface of the cylinder 11 should be at the level of the loweredge of the sieve 7 or below it; the upper surface of the cylinder 11should extend above the upper edge of the overflow 6.

In the case of the form of execution according to MG. 2, only thedispersion of the grinding stock passing through the sieve 7 or 7a or712 sealed on the shaft or closely adjoining the shaft comes intocontact with the surrounding gas. The rate of discharge of thedispersion of the grinding stock is selected so that the turbulencetransmitted to it by the stirring operation has been damped to theextent that an aspiration of gas will have been eliminated. The upperedge of the overflow 6 is preferably at least 3 cm. above the upperextremity of the sieve. This type of execution is especially suitablefor viscous dispersions of the grinding stock.

In the case of the forms of execution according to FIGURES 3 to 5, theair or gas aspiring turbulence of the grinding mixture is eliminated bylimiting the extent of the interface between the dispersion of thegrinding stock 9 and the air or gas to the interfacial area at thedischarge outlet; moreover, the flow of the dispersion of the grindingstock counteracts the aspiration of gas or air.

When the agitation is effected by vibration, the grinding space contains10 to 50, and preferably to 40% of the solid volume of the grindingelements, and use is made of the stirrer plates normally encountered invibro mixers, where the discs 4 should be fitted so that the narrow endsof the conical apertures point towards the charge inlet, i.e. theireffect opposes the direction of the throughput. The distance between themixing elements and the grinding vessel once again depends on thediameter of the grinding elements in each case and generally amounts tobetween 3 and 10 times the diameter of the grinding elements.

The following may inter alia be mentioned as materials containingsilicon dioxide suitable as the grinding elements: quartz, for instanceany type of sand which satisfies the above criteria in respect ofdimensions and shape such as Ottawa sand, and also glass and ceramicmasses provided that their surface is not porous, such as porcelain andsteatite, and other sintered metal silicates insoluble in water such asaluminum silicate.

The diameter of the coarse fraction of the solids to be dispersed shouldnot in general exceed 30% of the mean diameter of the grinding agentsand it should preferably be less than 10% of the mean diameter. Thefollowing may be mentioned, inter alia, as solids insoluble or barelysoluble in Water which can be dispersed: inorganic solids such asflowers of sulphur, red phosphorus, kaolins and other soft silicates,inorganic catalysts such as vanadium pentoxide and manganese dioxide,inorganic pigments such as iron oxides, titanium dioxide and cadmiumsulphides, organic compounds such as intermediate products insoluble inwater before or during a reaction, in particular coupling components forthe preparation of azo dyestufls insoluble in water, organic pestcontrol agents and plant protection agents, organic pharmaceuticals suchas analgesics, sulphonamides, antibiotics and contrast agents. Theprocess is of particular interest for grinding organic dyestuffs, suchas pigments, dispersion dyestuffs and vat dyestuffs, as Well as organicwhiteners insoluble in water.

In order to supplement the stability of the dispersion or to promote thegrinding action, the following surface active agents are added in aproportion of 0.1 to 200%, referred to the weight of the solid, to the lto 80%, and preferably 10 to 50% aqueous suspensions or extruded pastesof the solids. In the case where grinding is carried out in machines inwhich a strong air or gas aspiring turbulence is caused at the interfacebetween the dispersion of the grinding stock or the grinding mixture andthe air or gas, it is convenient to employ the alkali metal or alkalineearth metal salts of dinaphthylrnethane-2,2'-disulphonic acid, ofp-toluene-sulphonic acid and of polystyrene-sulphonic acid (molecularweight 10,000-l5,000) and polyvinyl-pyrrolidone (molecular weight10,000-

30,000) as the surface active agents. Provided that this will notinterfere with the further application of the dispersion of the solids,these may also be processed with up to 10%, calculated on the amount ofsolid to be dispersed, of the alkali metal salts of spent sulphidecellulose liquor and its amine condensation products or with thecondensation product from cresol-formaldehyde resin and the wsulpho acidobtained from 2,6-naphthol-sulphonic acid in combination with 1 to 2% ofa defoaming agent, referred to the amount of solid.

In the types of apparatus in which an interference by gas aspirationinto the grinding mixture has been eliminated, the following may beadded as the surface active products: All types of non-ionic emulsifyingagents, such as polyalkoxylated carboxylic acids, alcohols, phenols,amines and mercaptans with a higher molecular Weight, as well as anionicdispersing agents such as the alkali metal, ammonium and in some casesalso the alkaline earth metal salts of carboxylic acids, sulphonic acidsand sulphuric acid esters with a higher molecular Weight, and alsocationic emulsifying agents such as the salts of primary, secondary andtertiary amines of higher molecular weight with hydrohalide acids andsulphuric acid and in particular their quarternary ammonium compounds;it is also possible to employ surface active agents of the betaine typesuch as aminosulphonic acids with ahigher molecular weight, where thecarbon skeleton in their hydrophobic portion with a higher molecularweight may be interrupted by heteroatoms.

The following examples are given for the purpose of illustrating theinvention.

Example 1 A homogeneous paste is prepared from 250 g. of coarsely groundflowers of sulphur, having a particle distribution with a main fractionof diameters at about 50,11, larger fractions at about 15 1. and smallerfractions at about 6;; and respectively, by stirring them with cc. ofwater and 50 g. of the sodium salt, of dinaphthylmethane-2,2-disulphonic acid as the dispersing agent. This paste is mixed with970 g. of glass balls (specific gravity 2.97) of diameter 0.45 to 0.75mm. each of which does not (litter in its radius by more than 11% fromthe mean radius of the balls, as the grinding elements in the followingdevice. The latter consists of a vertical cylindrical vessel closed atthe bottom, open at the top and externally cooled, with a diameter of 10cm. and a height of about 20 cm. (internal dimensions) into which astirrer shaft extends vertically and centrally, three plane circulardiscs of thickness 0.5 cm. and with a diameter of 7.6 cm. being fittedhorizontally to the shaft on top of each other at a spacing of 2.7 cm.as the mixing elements. The free clearance between the lowest disc andthe bottom is 1 cm. and the rate of rotation is 3000 revolutions perminute. After it has been in operation for 1 hour, the particledistribution of the flowers of sulphur in the paste, which is separatedfrom the grinding elements by means of a sieve, comprises a mainfraction at 1 to 2 a larger fraction at 0.3 to In and a smaller fractionat 2 to 3 The increase in volume of the dispersion of the grinding stockowing to foam amounts to about 40%.

When flowers of sulphur are subdivided with glass balls in the range of1.8 to 2.2 mm. as the grinding elements under conditions which areotherwise the same, the resultant particle distribution of the'fiowersof sulphur has a main fraction at 2 to 3, and moderate fractions at l to2 and at 3 to 5 When the glass balls have a diameter of 2.7 to 3.1 mm.,the main fraction is at 5 to 6 moderate fractions are at 6 to 10p. andonly small fractions at less than 2n.

When a mixture of equal parts of glass balls with diameters of about 1,2, 3, 4, 5, 6, 7 and 8 mm. is employed as the grinding element, theparticle distribution of the flowers of sulphur achieved underconditions which are otherwise the same has a main fraction at 2 to 5,u,moder- 7 ate fractions at to small fractions at about 1p. and individualparticles at up to p.

Example 2 When flowers of sulphur are subdivided by the use of Ottawasand as the grinding element under conditions which are otherwise thesame as in Example 1, the sand having rounded edges and individualgrains whose radii differ by :2 toi25% from the mean radius of theseparate particles but its size being the same as that of the glassballs, the resultant particle distribution of the flowers of sulphur hasa main fraction at 1 to 211., large fractions at 0.5 to 1 and at 2 to 3and a small fraction at 3 to 4 When quarry sand with sharp edges andwith individual grains whose radii differ by 18 to :40% from the meanradius of the separate particles is employed as the grinding element,grinding becomes impossible since the grinding mixture sets solid.Grinding only becomes possible again when about 100 cc. of water areadded.

Example 3 When flowers of sulphur are subdivided under the sameconditions as those described in Example 1 except for the use of 50 g.of the sodium salt of polystyrene-sulphonic acid (molecular weight about13,000) as the dispersing agent, the increase in the volume of thedispersion of the grinding stock due to foam amounts to about 10 to 15%and the particle distribution of the flowers of sulphur is almostentirely at less than 1a, with very small fractions at 1 to 4p.

On the other hand, when the operation is carried out by employing as thedispersing agent the reaction product of hydroxydiphenyl and benzylchloride to which 12 to 14 moles of ethylene oxide had been added permole, on average, the increase in volume of the dispersion of thegrinding stock due to foam amounts to about 100%, and the particledistribution of the flowers of sulphur has a main fraction at 4 to 5 andmoderate fractions at 2 to 4 and at 5 to 10p. 7

Example 4 When grinding of the flowers of sulphur is carried out withthe ethylene oxide addition product of hydroxydiphenyl by the methoddescribed in Example 5 except that the operation is conducted in anappliance which corresponds to that in Example 1, though in this case alightweight plate sealed on the shaft and on the grinding ves sel isplaced over the grinding mixture so as to prevent the entry of air, theresultant particle distribution of the flowers of sulphur has a mainfraction at less than 1p. and only small fractions at 1 to 51.0.

Example 5 400 g.of a 36% aqueous suspension of the vat dyestuffIndanthrene Brown R (Schulz, Farbstoiftabellen, 7th edition, No. 1227)present in a state of subdivision with a main fraction at 3 to 8a, witha large fraction at 8 to 40,41. and a small fraction at 1 to 3 and whichcontains'10%, referred to the dyestuff, of the sodium salt ofpolystyrene-sulphonic acid with a molecular weight of about 13,000, aremixed during 15 minutes with 970 g. of glass balls having diameters of0.6 to 0.9 mm. in a device like that described in Example 1. The stateof fine subdivision of the dyestuff in the resultant dispersion of thegrinding stock consists of a main fraction at 2 to 3a, a large fractionat 1 to 2 and a small fraction at 3 to 4p.

-Example 6 370 g. of a 35% aqueous dispersion of copper phthalocyaninein the OC-mOdifiCatlOIl, prepared in accordance with German patentspecification No. 1,136,303 at a state of subdivision with a mainfraction of particles at 7 to 25 and which contains 10%, referred to theweight of the pigment, of the sodium salt of dinaphthylmethane-2,2'-disulphonic acid, are mixed with 970 g. of glass balls with thedimensions of 0.7 to 1 mm. as the grinding elements in the followingdevice. The latter consists of a vertical cylindrical vessel, closed atthe bottom, open at the top and externally cooled, with a diameter of 10cm. and a height of about 20 cm. (internal dimensions), into which astirrer shaft extends vertically and centrally which carries a verticalflat paddle stirrer of height 10 cm. and width 7 cm. as the mixingelement. The free clearance from the bottom is 1 cm. and the rate ofrotation is 1000 revolutions per minute. After it has been in operationfor 30 minutes, the particle distribution of the pigment comprises amain fraction at 0.5 to 1 large frac tions at less than 0.5 1 and at 1to 2 and a small frac? 200 cc. of an aqueous suspension of 30 g. ofcopper phthalocyanine in the Dt-lTlOdlfiCfitlOIl, prepared in accordancewith Example 1 of German patent specification No. 1,136,303, Whose mainfraction consists of particles at 7 to 25 are mixed for 1 hour at afrequency of cycles per second and an amplitude of 3 mm. together with 9I g. of the sodium salt of dinaphthylmethane-2,2'-d.isulphonic acid andwith 300 g. of glass balls with a diameter of 0.5 to 0.75 min. in acylindrical vessel, open at the top, with a diameter of 7 cm. and aheight of 15 cm. (internal dimensions) with the aid of a vibro mixerhaving a perforated circular disc of thickness 2.4 mm. and of diameter5.4 cm. provided with 20 conical drillings uniformly distributedthroughout the disc, their largest diameter being 9.0 mm. and theirleast diameter being 5.2 mm. The main fraction of the particles in thispigment is at less than 3 and a few individual particles at up to 61.1.are also present.

Example 8 1 hour with 500 g. of glass balls with diameters of 0.65

to 0.9 mm. as the grinding elements in a vessel of 1 litre capacitywhich is placed on a vibrating mill (Ulhnanns Encyclopiidie dertechnischen Chemie, 3rd edition, volume I, page 725). The resultantstate of fine subdivision comprises a main fraction at 1 to 2 and .alarge fraction at 3 to 4,1. g

When use is made of balls at 4.8 to 5.3 m-m., the resultant state ofsubdivision only comprises a main fraction at 4 to 10 larger fractionsat 2 to 4 and at 10'to 14g. and merely small fractions at less than 2;.

Example 9 240 g. of the compressed filter cake which contains 50 g. ofthe azo pigment dyestuff from 2,4,5-trichloroaniline and naphthol AS-Dare stirred intensively in a cylindrical mixing vessel having a usefulvolume of 1 litre with 75 g. of the sodium salt ofdinaphthylmethane-2,2-disulphonic acid and treated with 300 g. of glassballs with a diameter of 0.6 to 0.8 mm. The mixing vessel is now placedinto a vibrating mixer Turbula System Schatz (described inPharrnaceutika Acta Helvetial 37 [1962], pp. 529-543) and shaken for 2hours. The dyestufl had a particle distribution at 2 to 10 prior to thetreatment, with small fractions at 20 1.. After the treatment, the

particle distribution of the dyestufi was between 0.3 and 3p.

Example 10 20 kg. of a 10% aqueous paste of the dispersion dyestutfobtained by the mixed bromination of 1,5-diamino-4,8-dihydroxy-anthraquinone in accordance with German patentspecification No. 1,029,506 at an initial particle distribution with amain fraction at 8 to 15p, large fractions at 2 to 8 and at 5 to 50,1,and a very small fraction at l to 2 and which contains 150%, referred tothe weight of the dyestutf, of the sodium salt ofdinaphthylmethane-2,2'- disulphonic acid as the dispersing agent arestirred with 50 kg. of glass balls with a diameter of 0.9 to 1.2 mm. for6 hours in a mixer of the following construction. The latter consists ofa closed cylindrical vessel inclined to the horizontal at an angle of 15and having a diameter of 60 cm. and a height of 70 cm. (internaldimensions) which has been provided on its internal wall with two mixingfins of height 10 cm. and length 70 cm. positioned opposite each other,parallel with the axis and pointing towards the axis; its rate ofrotation is 20 revolutions per minute. The subsequent fine subdivisionof the dyestufi is at less than 4,u.

Example 11 The organic substance obtained in accordance with Example 1of German patent specification No. 1,080,963 which is hardly soluble inwater and has a particle distribution'with a main fraction at 10 to 15 alarge fraction at 1 to 6p. and a small fraction at 15 to 40,44 is pumpedin the form of its 40% aqueous suspension, with a content of referred tothe weight of solid to be subdivided, of the sodium salt ofdinaphthylmethane-Z,2-disulphonic acid and 1%, referred to the weight ofsolid to be subdivided, of a silicone defoaming agent, at a uniformspeed of 100 litres per hour through the following device. The latter isconstructed in accordance with FIGURE 1, where the mixing elements 4 and4a are plane circular discs, the cylinder 11 being missing, and thedischarge level is at the level of the lower edge of the sieve. Thedimensions of the grinding vessel are height 100 cm. and diameter 26 cm.(internal dimensions), and those of the discs are diameter 21 cm. andthickness 1 cm. The lowest disc is spaced 2 cm. clear of the bottom andthe uppermost disc 4a is at the level of the lower edge of the sieve,with 9 other discs spaced at equal distances between them in theirattachment to the shaft. The shaft rotates at a rate of 1000 revolutionsper minute, and the grinding vessel contains 67 kg. of glass balls witha diameter of 0.5 to 0.75 mm. After it has been passed through twice,the resultant particle distribution comprises a main fraction withparticles at 1 to 1.5 larger fractions at 0.5 to 1 and at 1.5 to 2 aswell as traces at 2 to 2.5,u.

Example 12 A 35% aqueous suspension of CI. Pigment Yellow 3 (ColourIndex, 2nd edition, 11, 710) which conveniently contains 0.04% ofpolyglycol-modified oleic acid (1216 moles of ethylene oxide per mole ofacid) and 0.36% of the sodium salts of sulphochlorination products ofhigher hydrocarbons originating from the preparation of the pigment,which has a particle distribution with a main fraction at l to 3 largefractions at 3 to 7,u, small fractions at 0.5 to 1p. and at 7 to 40 andwhich has been treated with 10%, referred to the weight of the pigment,of the sodium salt of dinaphthylmethane-2,2-disulphonic acid, is pumpedthrough the following device at a uniform rate of throughput amountingto 27 litres per hour. The latter is constructed in accordance withFIGURES 2 to 5, where the grinding vessel has a diameter of 15 cm. and aheight of 28 cm. (internal dimensions) and the sieve 7b has a height of3 cm.; in the case of a construction according to FIG. 2, the lowestpoint of the overflow 6 is 3 cm. above the sieve 7a. 7 circular discswith a diameter of 12 cm. and a thickness of 0.6 cm. are fitted as themixing elements at equal distances to the shaft 3 of thickness 2.6 cm.so that the disc next to the charge inlet 5 is spaced 1 cm. clear fromthe bottom and so that the disc next to the sieve 7a has a clearance of3 cm. from the latter. The seals 10 are slip rings. The shaft rotates at1650 revolutions per minute. The grinding vessel 1 contains 7 kg. ofglass balls with diameters of 0.55 to 0.85 mm. The sieves 7a and 7b havea free mesh width of 4 mm. The paste free from foam which is therebyobtained and can therefore be readily further processed contains thepigment in a state of fine subdivision with a main fraction at 1 to 2large fractions at 0.5 to I r and at 2 to 4 and small fractions at 4 to5 When a subdivision of the yellow pigment is attempted in a device ofthe same dimensions but where the construction is in accordance withFIGURE 1, when the mixing element 4a also represents a circular disc ofdiameter 12 cm. whilst the cylinder 11 is missing, the discharge levelis at the level of the lower edge of the sieve and the sieve has aheight of 12 cm. the operation proves to be impossible since thegrinding mixture (dispersion of the grinding stock and the grindingballs) spills over the upper edge of the sieve after a short while owingto the resultant stable foam.

When silicone defoaming agents were added, it was still impossible toachieve a satisfactory result of the experiment.

Example 13 A 62.5% aqueous suspension of flowers of sulphur at aparticle distribution with a main fraction at about 5011., largerfractions at about 15 and smaller fractions at 6,11. and at 80,1, whichcontains 20%, referred to the weight of the sulphur, of the sodium saltof dinaphthylmethane-2,2'- disulphonic acid is pumped at a uniform rateof throughput of 15 litres per hour through devices like those describedin Example 12 and constructed in accordance with FIGURES 25. Theresultant state of fine subdivision of the sulphur comprises a mainfraction at 2 to 411, large fractions at 0.5 to 2 and at 4 to 5,u, andsmall fractions at 5 10 6,11

When the same experiment is carried out in a device with the samedimensions but where the construction is in accordance with FIGURE 1,when the mixing element 4a also represents a circular disc of diameter12 cm. whilst the cylinder 11 is missing, the discharge level is at thelevel of the lower edge of the sieve and the sieve has a height of 12cm., the resultant increase in the volume of the discharged dispersionof the grinding stock is 35%, compared with that of the chargeddispersion of the grinding stock, even when 1% of a silicone defoamingagent has been added (calculated on the sulphur content). The resultantparticle distribution of the sulphur has a main fraction at 7 to 10large fractions at 5 to 7,u and at 10 to 15 and small fractions at 1 to5p. and at 15 to 25 Example 1 4 When a subdivision of the flowers ofsulphur is carried out under the same conditions as described in Example13 in a device with the same dimensions but where the construction is inaccordance with FIGURE 1 when the cylinder 11 has a diameter of 12 cm.and a height of 10 cm., its lower surface being at the level of thelower edge of the sieve 7, the sieve 7 has a height of 12 cm. and thehighest point of the overflow 6 is 5 cm. above the lower edge of thesieve 7, the increase in volume of the discharged dispersion of thegrinding stock due to the foam amounts to 15 to 20% of the volume of thecharged dispersion of the grinding stock. The resultant state of finesubdivision of the sulphur comprises a main fraction at 5 to 6 largerfractions at 2 to 5 1 and at 6 to 8 2, and small fractions at 1 to 2 andat 8 to 10 Example 15 A 30% aqueous suspension of copper phthalocyaninein the tit-modification, prepared in accordance with German patentspecification No. 1,136,303 at a particle distribution with a mainfraction at 7 to 25 and which contains 20%, referred to the pigmentcontent,of the sodium salt of dinaphthylmethane-Z,2-disulphonic acid and50%, referred to the pigment content, of the sodium salt of the anilinecondensation product of lignin-sulphonic acid is pumped through deviceslike those described in Example 12 and constructed in accordance withFIGURES 2-5, at a uniform speed of 15 litresper hour. The resultantstate of fine subdivision of the pigment comprises a main fraction at0.5 to 2 large fractions at 0.3 to 0.5 1 and at 2 to 5p, and smallfractions at 5 to 611..

When the same experiment is carried out in a device with the samedimensions but where the construction is in accordance with FIGURE 1,when the mixing element 4a also represents a circular disc of diameter12 cm. whilst the cylinder 11 is missing, the discharge level is at thelevel of the lowest edge of the sieve and the sieve has a height of 12cm., the resultant increase in the volume of the discharged dispersionof the grinding stock is 110%, compared with the volume of the chargeddispersion of the grinding stock. The resultant particle distribution ofthe pigment comprises a main fraction at 4 to large fractions at 2 to 4and at 10 to 13p, and small fractions at 1 to 2 and at 13 to 15 What weclaim is:

Apparatus for continuously dispersing solids in a liquid medium whichcomprises a hollow vessel having a sieve therein, which sieve dividessaid vessel into a grinding zone and a residence Zone; an inlet openingin said hollow vessel in the grinding zone portion thereof and an outletat the residence zone portion thereof; wherein said residence zone isdefined by said sieve, said outlet and walls along all other surfacesthereof, whereby to exclude air from contact with the contents of saidresidence zone; said outlet being disposed at a point of said apparatuswhich is the highest point in said residence zone and higher than saidinlet and being operatively associated with an outlet tube having amultiple bend therein, which tube has an exit which is disposed at apoint lower than said outlet, but higher than said inlet.

References Cited UNITED STATES PATENTS 2,855,156 10/ 1958 Hochberg 241223,050,263 8/1962 Barkman 241172 X 3,149,789 9/1964 Szeguari 241172 X3,172,609 3/1965 Olsen 241172 X 3,215,353 11/1965 Goeser 241172 X3,243,128 3/1966. Tight 241172 X ANDREW R. JUHASZ, Primary Examiner.

GERALD A. DOST, HARRY F. PEPPER, JR.,

' Examiners.

